1. Field of the Invention
The present invention is broadly concerned with biodegradable and edible packaging composites or containers comprising self-sustaining bodies and formed from a mixture comprising a non-petroleum based, biodegradable adhesive and a quantity of fiber. More particularly, the containers comprise a fiber derived from a fiber source selected from the group consisting of straw (e.g., wheat, rice, barley), corn stalks, sorghum stalks, soybean hulls, peanut hulls or any other fibers derived from grain milling by-products), and mixtures thereof. The adhesive can be protein-based or starch-based, and is preferably formed by modifying a protein, starch, or protein-rich flour with a modifier comprising alkaline materials and/or modifiers having particular functional groups. The resulting mixture has a low moisture content and is molded at high temperatures and pressures to yield a final container having high compressive strengths.
In another aspect of the invention, molding apparatus and corresponding methods are provided for forming complex shapes using composite-type molding materials which are non-flowable under pressure, such as polymer-impregnating cellulosic fibers. The preferred equipment includes generally annular male and female mold sections which present cooperating adjacent surfaces when telescoped together for compression of the non-flowable molding materials so that the materials assume a desired shape for molding. In preferred forms, the mold sections are heated to accelerate curing and hardening of the molding materials.
2. Description of the Prior Art
Livestock gel blocks are currently utilized for supplementing the diets of sheep, horses, and cattle in both feedlot and open grazing conditions. The blocks are formed of gels which are flowable at a temperature of about 80xc2x0 C. These gels are poured into a container and become rigid upon cooling. The gel blocks have xe2x80x9ccold flow propertiesxe2x80x9d meaning that, although they appear to be a solid, the blocks will not retain their shape when subjected to stress (such as from the weight of other blocks or gravity). As a result, the gel blocks are not free-standing and must be in a container at all times. The gels turn into a thick syrup upon absorbing moisture from the air. This syrup is then consumed by the livestock.
Currently available containers for use with gel blocks include half steel drums, plastic tubs, and paper or cardboard containers. Each of these containers has undesirable properties. For example, the steel drums must be either thrown away or recycled after use. Recycling is generally preferred in order to minimize the quantity of waste in landfills and other disposal sites. However, recycling involves additional labor and expense as the drums must be collected and transported back to the feed manufacturer and then reconditioned (i.e., reshaped, cleaned, and sterilized) by the manufacturer before reusing the drum. Likewise, plastic tubs can be discarded or recycled but must undergo the same labor and expense involved in recycling steel drums. Furthermore, the plastic tubs result in the generation of plastic waste which presents a disposal problem for the consumer as well as a liability problem for the manufacturer.
Paper and cardboard containers have been attempted commercially as an alternative to plastic or steel. However, paper and cardboard containers do not perform adequately. One problem with paper and cardboard containers is that they are permeable to moisture at room conditions, thus allowing moisture to contact the gel. This causes the gel to turn into a syrup prematurely which then seeps through the container, making the products difficult to ship and store. Furthermore, these paper and cardboard containers do not easily biodegrade, leaving waste at the feeding site. Finally, the livestock may consume portions of these paper or cardboard containers, presenting a possible danger to the livestock if the paper or card-board is not processed following FDA standards.
U.S. Pat. No. 5,160,368 to Begovich discloses a biodegradable package for fast food comprising a body which is molded from a composition consisting essentially of an admixture of biodegradable natural materials comprising low-protein flour (i.e., about 10-15% by weight protein in the flour) or meal from edible gramineous plants (e.g., corn or sorghum), crushed hay of gramineous plants (e.g., wheat, sorghum, corn, or corncob leaves), a preservative, and a plasticizing agent. However, the ""368 package has a high moisture content prior to molding (about 50% by weight moisture), thus resulting in a container that often cracks when molded at the high temperatures and pressures necessary to obtain a strong container. Furthermore, the ""368 patent fails to use a strong adhesive which results in a package having inadequate mechanical properties for use in packaging of livestock feed gel blocks (which often weigh 250 lbs. each) and other applications which require a strong container.
Particle boards and similar composites are typically formed from wood chips, sawdust and other wood waste products by mixing such cellulosic materials with a synthetic resin binder and pressing the mixture between flat platens under high pressures and elevated temperatures. While this method is useful for making flat panels, it is not suitable for production of non-planar shapes such as frustoconical half-barrel sections or other complex shapes.
Injection molding processes have long been used to form non-planar objects of varied shapes. However, injection molding is only applicable when the starting molding material is at least somewhat flowable under heat and pressure conditions. Thus, injection molding is inapplicable for use with relatively light, particulate, substantially dry starting materials such as those used to form particle board or the like.
There is a need for biodegradable and edible packaging containers which do not contain cracks or other defects and which have strong mechanical properties, allowing the container to be subjected to stress with little risk of failing. Also, improved molding apparatus and methods which can make use of relatively inexpensive dry particulate starting materials while having the capability of producing non-planar complex objects would represent a significant advance in the art.
The instant invention provides biodegradable and edible composites having high compressive strengths. Broadly, the composites are in the form of a self-sustaining body formed from a mixture comprising a non-petroleum based, biodegradable adhesive and a quantity of fiber. These composites can be used as containers for livestock gel blocks as well as other applications such as flower and plant containers.
In more detail, the fiber utilized in the inventive composites is derived from a fiber source selected from the group consisting of straw (including wheat, rice, and barley), corn stalks, sorghum stalks, soybean hulls, peanut hulls, and mixtures thereof. While most non-petroleum based, biodegradable adhesives which are capable of forming the high strength composites of the invention are suitable, it is preferred that the adhesive be formed by modifying a starch (e.g., cereal starch and legume starch), protein, protein-rich flour (i.e., soy flour or other flour having at least about 25% by weight protein, and preferably at least about 40% by weight protein), or mixtures thereof with a modifier selected from the group consisting of:
(1) alkaline materials (such as NaOH);
(2) saturated and unsaturated alkali metal C8-C22 (and preferably C10-C18) sulfate and sulfonate salts;
(3) compounds having the formula I: 
xe2x80x83wherein each R is individually selected from the group consisting of H and C1-C4 saturated and unsaturated groups, and X is selected from the group consisting of O, NH, and S; and
(4) mixture of (1), (2), and (3).
The C1-C4 saturated and unsaturated groups refer to alkyl groups (both straight and branched chain) and unsaturated refers to alkenyl and alkynyl groups (both straight and branched chain). Preferred compounds having the formula I are urea and guanidine hydrochloride. When urea is the modifier, the protein, starch, or protein-rich flour is preferably essentially free of urease, having less than about 10 activity units of urease. Alternately, a urease inhibitor can be added to the protein, starch, or protein-rich flour.
Saturated alkali metal C8-C22 sulfate and sulfonate salts include all alkali metal alkyl (such as octyl and dodecyl) C8-C22 sulfate and sulfonate salts. Unsaturated alkali metal C8-C22 sulfate and sulfonate salts include all alkali metal alkenyl (such as decenyl and octadecenyl) C8-C22 sulfate and sulfonate salts and all alkali metal alkynyl (such as octynyl and tetradecynyl) C8-C22 sulfate and sulfonate salts. Two particularly preferred modifiers in this class are sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS).
The adhesives are prepared by simply forming an aqueous slurry or dispersion of modifier and starch, protein, or protein-rich flour. This modifier slurry is mixed for about 1-400 minutes at a temperature of from about 15-70xc2x0 C. Preferably, the forming and mixing of the dispersion takes place under ambient temperature and pressure conditions.
The resulting adhesive is then mixed with a quantity of fiber. Preferably the particle size of the fiber is such that less than about 10% of the particles have a particle size of less than about 678 xcexcm. The fiber and non-petroleum based adhesive should be utilized in appropriate quantities so that the mixture and final composite or container comprises from about 5-20% by weight adhesive solids (i.e., all solid components in the adhesive on a dry basis), and preferably from about 10-16.7% by weight adhesive solids, based upon the total weight of the mixture or final composite taken as 100% by weight. The mixture and final composite or container preferably comprises at least about 70% by weight fiber solids, and preferably from about 80-95% by weight fiber solids, based upon the total weight of the mixture or final composite taken as 100% by weight. The ratio of fiber solids to adhesive solids should be from about 2.5:1 to about 20:1, preferably from about 4:1 to about 15:1, and more preferably from about 5:1 to about 9:1.
The formed mixture is then dried to a moisture content of less than about 20% by weight, preferably from about 5-15% by weight, and more preferably about 11-13% by weight, based upon the total weight of the mixture taken as 100% by weight. It is preferred that no preservatives be added to this mixture so that the final composite is essentially free of preservatives. In one embodiment, the mixture consists essentially of a non-petroleum based, biodegradable adhesive and a quantity of fiber.
When a protein or protein-rich flour is modified to form the biodegradable adhesives utilized in preparing the composites of the invention, the protein or protein-rich flour should be included in sufficient quantities so that the concentration of protein in the mixture (i.e., the fiber mixed with the aqueous dispersion after drying) is at least about 5% by weight, preferably at least about 7% by weight, and more preferably at least about 9% by weight, based upon the total weight of the mixture taken as 100% by weight. Suitable proteins for forming the adhesives include those selected from the group consisting of soybean protein, wheat protein, corn protein, sorghum protein, and mixtures thereof.
The dried mixture is then molded into a package having the preferred shape for the particular application. Molding is carried out by subjecting the shaped mixture to molding temperatures of from about 150-500xc2x0 F., and preferably from about 200-350xc2x0 F., and molding pressures of from about 150-600 psi, and preferably from about 220-450 psi. The molding process should be carried out for a time period of from about 1-20 minutes, and preferably from about 3-8 minutes. Molding can be carried out on any conventional molding presses known in the art, so long as the press is able to accommodate the foregoing temperature and pressure conditions. Furthermore, the mixture can be molded into virtually any shape, depending on the particular application. Preferred shapes for use in livestock feed supplements include box-shaped and half-barrel-shaped containers.
The final, molded composite or container should have a moisture content of less than about 10% by weight, and preferably less than about 5% by weight, based upon the total weight of the composite or container taken as 100% by weight. The final composite or container should have an ASTM D1037-93 compressive strength of at least about 5 MPa, preferably at least about 8 MPa, and more preferably at least about 10 MPa. Furthermore, the biodegradable composite or container should be essentially decomposable within about 1 year of being placed in the environment, depending upon its exposure to moisture and/or light. Finally, a moisture barrier (such as an FDA food grade wax) can be applied to the surfaces of the formed composite so as to minimize moisture absorption by the composite.
The present invention also provides molding apparatus broadly including generally annular male and female mold sections together with a support assembly for supporting the male section in general concentric alignment with the female section. Preferably, the female mold section includes a base and a generally annular sidewall assembly coupled to the base which presents substantially concentric, generally annular inner and outer sidewalls defining therebetween a space for receiving a molding material. The male mold section includes a generally annular sidewall unit adapted to telescope within the female mold sidewall assembly. The mold support assembly includes a drive operable to selectively move at least one the male and female mold sections to effect telescoping thereof. Respective portions of the sidewall unit and at least one of the inner and outer sidewalls of the female sidewall assembly are arranged to cooperatively compress the molding material during telescoping of the mold sections, in order that the molding material assumes a desired shape. Preferably, the male and female mold sections have wall portions which are cooperatively tapered, usually at an angle of taper of from 2-20xc2x0, most usually about 5xc2x0.
Preferably, a heating assembly is provided to heat the molding material during the molding operation to accelerate curing and hardening thereof. This heating assembly may include resistance heating elements operably coupled with the female mold sidewall assembly and the male mold sidewall unit. Alternately, other types of heaters could be employed, e.g., oil, water or steam.
Although not essential, in most cases the male mold section is situated above the female mold section and in substantial concentric alignment therewith. The mold drive preferably includes a hydraulic ram coupled with the male mold section for forcibly telescoping the male mold section at least partially into the female mold sidewall assembly. In this type of molding apparatus, a lower frame is provided beneath the female mold section and allows selective movement of the latter between a molding location beneath the male mold section and a load/unload location shifted away from the molding location.
In further preferred aspects of the invention, the female mold section receives an annular liner which accommodates the molding material and also receives the male mold section. In addition, a molded article detach device is operable coupled with the male mold section so that, upon retraction of the male mold section after a molding operation, the molded article can be easily detached from the male mold section.
In operation, a quantity of molding material is placed with the female mold section and the mold drive is operated to cause relative movement between the male and female mold sections so that the sidewall unit of the male section telescopes into the sidewall assembly of the female section; during such movement the molding material is compressed between respective portions of the sidewall unit and at least one of the inner and outer sidewalls of the female mold section. At this point, a predetermined time-temperature molding cycle is carried out to harden and cure the compressed molding material, whereupon the mold sections are separated and the molded article is recovered.
While in preferred embodiments the mold sections are substantially annular in configuration, the invention is not so limited. That is, polygonal (e.g., rectangular or hexagonal) in cross-section mold walls can be provided, so as to produce similarly configured final molded articles.
The molded articles of the invention find utility in a number of contexts. For example, low-moisture type livestock feed supplements are not free standing but must be contained in some type of package. Currently utilized feed supplement containers include half steel drums, plastic tubs and paper board or fiber board containers. However, the molded products of the invention, preferably made using cellulosic materials, are fully biodegradable or edible and thus present no recovery or disposal problems after usage. Another use would be in one-way xe2x80x9cdisappearingxe2x80x9d consumable containers used by the military to transport material to remote locations. As these supplies are used, the containers could be left behind for decomposition or consumption by wildlife in a relatively short time. This would eliminate the burden of transporting empty containers while also ameliorating the negative environmental impact of remote military operations. Finally, molded products made using the apparatus of the invention can serve as compostable barrels for yard waste and plantable tree containers.